The present invention relates in general to multi-frequency communications and, more particularly, to an apparatus, system, and method for enabling multi-frequency communication over a telephone network having a billing/tax tone.
The Public Switched Telephone Network (PSTN) was originally designed for carrying analog voice communication signals. The typical PSTN network includes numerous central offices. Communication between the central offices can be accomplished through high speed switched digital links. Local loops couple the central offices to the customer premises. The local loops can be analog networks of twisted pair copper wiring. These local loops are often referred to as the Plain Old Telephone System (POTS) network. A xe2x80x9ccustomer premises network,xe2x80x9d xe2x80x9cpremises network,xe2x80x9d or xe2x80x9cpremises wiringxe2x80x9d connects electronic devices within the customer premises to the local loop. A typical premises network includes twisted pair copper wiring coupled to RJ-11 phone jacks. As used herein, xe2x80x9ctelephone networkxe2x80x9d refers to the network as a whole, including the central offices, local loops, and premises networks.
Digital Subscriber Line (xDSL) technology can apportion the transmission of data over a POTS network into a voice channel and a digital channel. The voice channel can include signals below 4 kHz while the digital channel can include signals above 4 kHz. For example, Asymmetric Digital Subscriber Line (ADSL) technology apportions the voice channel as 500 Hz to 3.5 kHz and the digital channel as 25 kHz to 2 MHz. As such, xDSL can provide a method to increase the bandwidth of the existing telephone network infrastructure.
Furthermore, xDSL technology can allow conventional devices that use the voice channel, and high frequency devices xDSL devices such as xDSL transceivers, to couple to the same POTS network and communicate simultaneously, using the respective channels. Conventional electronic devices, include low frequency devices such as telephones, facsimile machines, and conventional computer MODEMs.
In order to allow a POTS network to simultaneously carry signals over the voice channel and the data channel, conventional xDSL installations typically employ one of two approaches to separate the two channels. One objective of each system is to isolate the low frequency devices from the large high frequency output of the high frequency devices. This isolation prevents disruption of communication over the voice channel.
The first approach includes using multiple splitters. At both the central office and the customer""s premises, a plain old telephone service splitter (POTS splitter) receives an input signal from a telephone line and separates a telephone signal (on the voice channel) and a data signal (on the data channel) from the input signal. The conventional POTS splitter includes a low-pass filter for separating the telephone signal from the input signal, and a high-pass filter for separating the data signal from the input signal. For example, in a typical ADSL installation, the low-pass filter of the conventional POTS splitter can pass frequencies below 4 kHz to the low frequency devices, while the high-pass filter can pass frequencies above 25 kHz to the high frequency devices.
A second conventional approach for separating the voice channel from the digital channel involves using a distributed filter at the customer premises end of an xDSL network. With a distributed filter architecture, a microfilter, is coupled between the premises network and each low frequency device that uses signals in the voice channel. For example, each telephone, facsimile machine, and other conventional telephony device would be coupled first to a microfilter filter which would then be coupled to the telephone network of the customer premises (e.g., via a standard telephone line). Typically, each microfilter includes a low pass filter that allows signals in the voice channel to travel to and from the low frequency devices, while filtering out traffic and noise caused by high frequency devices using the digital channel. In this scheme, devices using the digital channel, such as xDSL transceivers, can connect directly to the premises network.
The distributed or microfilter approach provides advantages over the POTS splitter approach by eliminating the need for installation of a POTS splitter at the customer premises. This eliminates the costly xe2x80x9ctruck rollxe2x80x9d to the customer premises, and makes the implementation of an xDSL network more economically feasible.
Problems result from both the POTS splitter and the distributed filter approaches if a telephone network uses frequency bands other than the voice channel to communicate with the low frequency devices. For example, in many European markets, a telephone network communicates a billing/tax tone to the frequency devices, typically over a 12 kHz or 16 kHz frequency. As used herein, billing/tax tone refers to a signal communicated to a low frequency device over a frequency outside the voice channel. Billing/tax tone frequency is the frequency at which the billing/tax tone is communicated.
A conventional POTS splitter or microfilter using a low-pass filter tuned at 4 kHz will prevent the billing/tax tone from reaching the low frequency equipment. Therefore, the conventional POTS splitters and microfilters cannot be employed in such an environment.
Additionally, telecommunication equipment manufacturers have been unable to design a cost-effective POTS splitter or microfilter to efficiently separate the various signals. Therefore, conventional approaches fail to enable the development of an xDSL network over telephone networks having billing/tax tones.
In accordance with the present invention, an apparatus, system, and method for enabling multi-frequency communication over a telephone network having a billing/tax tone are disclosed that provide significant advantages over prior developed systems. The present invention solves problems presented by the disruptive interaction of high frequency devices and low frequency devices at frequency ranges typically used for billing/tax tones.
According to one aspect of the present invention, an apparatus comprises a connection port operable to couple to a telephone network. An output port is coupled to the input port, and is operable to couple to a high frequency device. A trap is coupled between the connection port and the output port. The trap is tuned to isolate the high frequency device from the telephone network at a specified frequency range.
According to another of the present invention, a method includes receiving an input signal over a telephone network and isolating a high frequency device from the telephone network at a specified frequency range of the input signal.
According to a further aspect of the present invention, a system comprises a trap operable to couple between a telephone network and a high frequency device. The trap is tuned to isolate the high frequency device from the telephone network at a specified frequency. The system further comprises a filter is operable to couple between the telephone network and a low frequency device. The filter is tuned to isolate the low frequency device from the telephone network at a frequency above the specified frequency.
It is a technical advantage of the present invention that it prevents parasitic capacitance of a high frequency device, such as an xDSL transceiver, from attenuating a billing/tax tone at the specified frequency range. Therefore, multi-frequency communication, such as xDSL communication, is enabled over a telephone network having a billing/tax tone.
It is another technical advantage of the present invention that it allows for a distributed filter architecture at the customer premises end of an xDSL network. The invention eliminates an expensive xe2x80x9ctruck rollxe2x80x9d to each customer premises and enables the use of relatively inexpensive microfilters. An xDSL network is therefore much more economically feasible in countries having a telephone network that uses a billing/tax tone.
Other technical advantages should be apparent to one of ordinary skill in the art in view of the specification, claims, and drawings.